(1) Field of the Invention
The invention deals with the differentiation and segregation of wood fiber chips from bark fiber chips and wood-bark fiber chips.
(2) Description of the Prior Art
For our woodlands and forests to keep pace with the increasing demands of our society for more raw materials, more efficient utilization of the available wood fiber must be made.
One of the most efficient wood harvesting methods is total tree chipping, where the aboveground portion of the tree is reduced to wood chips, thin wood pieces of various widths and lengths. There are several stationary and portable whole-tree chippers commercially available, but none can debark the total tree prior to chipping. As a result, these chippers produce three types of chips: wood fiber chips, with no bark content; bark fiber chips, comprised solely of bark; and wood-bark fiber chips, comprised of both wood and bark.
There are several reasons for debarking wood fiber prior to utilization. The two most important are to increase the quality of wood fiber yield, and to remove contaminants such as rocks, dirt, grit, and soils, which are embedded in the bark during harvesting and transport. Formerly, debarking was done with axes, spuds, and draw knives. As technology progressed, machines replaced these hand tools. The mechanical debarkers are fairly efficient on stemwood, but cannot debark the limps and tops which can comprise up to 50 percent of the total tree fiber weight. If one adds to this the inherent inefficiency of present-day debarkers, it becomes apparent that an improved method of wood and bark separation is desirable.
For some products it is neither desirable nor necessary to remove the bark from the wood fiber. Bark in natural volumes is, however, intolerable in the manufacture of quality paper or chipboard products. The fact that "clean" wood fiber is desirable and that present-day technology is deficient in separating clean from bark-laden fiber provides the incentive for this invention.